The present invention relates to a scroll fluid machine suitable for use as an air compressor, a vacuum pump, etc. by way of example.
In general, a scroll fluid machine includes a fixed scroll member and an orbiting scroll member provided facing the fixed scroll member. The fixed scroll member and the orbiting scroll member each have a disk-shaped end plate and a wrap portion projecting axially from the end plate. The wrap portion is wound spirally from the radially inner side toward the radially outer side of the end plate. Thus, the fixed scroll member and the orbiting scroll member define a plurality of compression chambers by overlapping of their wrap portions.
In the scroll fluid machine, the orbiting scroll member is driven by a driving shaft to perform an orbiting motion with respect to the fixed scroll member with a predetermined orbiting radius, thereby sucking a fluid, e.g. a gas, from a suction opening provided in a radially outer part of the fixed scroll member, and successively compressing the fluid in the compression chambers. Finally, the compressed fluid is discharged to the outside from a discharge opening provided in a radially inner part of the fixed scroll member.
There is a conventional scroll fluid machine having recesses or projections on the peripheral surfaces of the wrap portions to reduce the gap between the wrap portions, thereby increasing the degree of hermeticity in the compression chambers and thus improving the compression efficiency [for example, see Japanese Patent Application Unexamined Publication (KOKAI) No. Hei 5-141379 and Journal of Technical Disclosure No. 2001-1746 issued by the Japan Institute of Invention and Innovation].
In the scroll fluid machine according to the prior art, a plurality of axially extending projections (or recesses) are formed on the peripheral surfaces of the wrap portions of the fixed scroll member and the orbiting scroll member. The projections are formed on each wrap portion at approximately equal spacings along the spiral direction, that is, the circumferential direction of the wrap portion, throughout it from the radially inner side toward the radially outer side.
Incidentally, the above-described conventional scroll fluid machine has a plurality of axially extending projections (or recesses) on the peripheral surfaces of the wrap portions to minimize the amount of compressed fluid leaking out through the mutually opposing wrap portions, thereby increasing the degree of hermeticity in the compression chambers.
However, the projections provided in the prior art scroll fluid machine have a quadrangular transverse sectional configuration. Accordingly, the tip of each projection is wide in width. Therefore, when the projections contact the mating wrap portion, some problems arise, such as an increase in power loss due to frictional resistance, and generation of loud noise, and occurrence of scoring.
Further, the projections are formed on each wrap portion at approximately equal spacings along the circumferential direction of the wrap portion throughout it from the radially inner side toward the radially outer side. Therefore, the pitch of the projections is too large to close hermetically the compression chambers at the radially inner side where the radius of curvature of the wrap portion is small. Consequently, the compressed fluid may leak out, leading to a degradation of the compression efficiency.
Further, in a region where a plurality of projections come closest to the mating peripheral surface with the same distance from the peripheral surface at a certain timing, the fluid flows from a high-pressure side compression chamber into a low-pressure side compression chamber through a very small gap formed between the projections and the mating peripheral surface. At this time, vortex motion of the fluid occurs, and noise is generated on the principle of wind instruments.
Accordingly, the prior art suffers from the following problem. During the operation of the scroll fluid machine, noises are simultaneously generated from a plurality of positions between the fixed scroll member and the orbiting scroll member. These noises may leak to the outside from the fluid suction opening, etc. in the form of a loud noise of high frequency, causing the machine operating environment to be deteriorated.
Further, in the prior art, the peripheral surface of the wrap portion is provided with a plurality of projections (or recesses) extending over the entire axial length of the wrap portion. Consequently, at the region of the peripheral surface of the wrap portion where no projections are present, the gap between the wrap portion of the fixed scroll member and the wrap portion of the orbiting scroll member is larger than in the case of a scroll fluid machine not provided with projections. Accordingly, the compression efficiency degrades undesirably.
The present invention was made in view of the above-described problems with the prior art.
A first object of the present invention is to provide a scroll fluid machine designed to enhance the mechanical strength of the projections provided on the wrap portion to increase the degree of hermeticity in the compression chambers and also designed to be capable of preventing power loss, noise generation and so forth during the operation of the scroll fluid machine.
A second object of the present invention is to provide a scroll fluid machine designed to be capable of minimizing the leakage of the compressed fluid to improve the compression efficiency.
A third object of the present invention is to provide a scroll fluid machine designed to be capable of improving the compression efficiency with the projections provided on the wrap portion while suppressing the generation of noise and so forth due to the projections and realizing a quiet and favorable operating environment.
The present invention is applicable to a scroll fluid machine including one scroll member having a wrap portion projecting axially from an end plate. The wrap portion is wound spirally from the radially inner side toward the radially outer side of the end plate. The other scroll member is provided facing the one scroll member. The other scroll member has a wrap portion projecting axially from an end plate. The wrap portion is wound spirally from the radially inner side toward the radially outer side of the end plate so as to overlap the wrap portion of the one scroll member to define a plurality of compression chambers.
According to a feature of the present invention, at least the one scroll member has on a peripheral surface of the wrap portion thereof a plurality of axially extending projections at spacings in the spiral direction of the wrap portion. Each projection has a transverse sectional configuration defined by the top of the projection and slopes connecting the top to the peripheral surface. Each slope has a concave surface at a portion thereof that is contiguous to the peripheral surface.
With the above-described arrangement, each projection is formed in an approximately triangular transverse sectional configuration. Therefore, it is possible to prevent stress concentration and to increase the mechanical strength at the tops of the projections. In addition, machining can be readily carried out by using a tool, e.g. an end mill. On the other hand, when contacting the opposing peripheral surface of the wrap portion of the other scroll member, the tops of the projections are readily crushed or worn. Therefore, the tops of the projections can become fit to the opposing peripheral surface of the wrap portion without strongly contacting it many times.
According to another feature of the present invention, the concave surface of the projections has a radius of curvature not less than that of a circular arc having a radius xc2xc times the radial turn spacing T of the wrap portion.
With the above-described arrangement, the projections can be formed with the same tool, e.g. an end mill, as used to cut the peripheral surface of the wrap portion. That is, the projections can be formed when cutting the peripheral surface of the wrap portion by using the same tool, e.g. an end mill, without the need for tool change.
According to another feature of the present invention, the projections satisfy the following condition:
W1xc3x972xe2x89xa6W2
where W1 is the width of the top, and W2 is the overall width of each projection.
With the above-described arrangement, the projections are widened at the root side thereof. Thus, the mechanical strength of the projections can be increased.
According to another feature of the present invention, the pitch of the projections in the spiral direction is narrow at the radially inner side but wide at the radially outer side.
With the above-described arrangement, a radially inner part of the wrap portion where the radius of curvature of the wrap portion is small and hence the curvature thereof is steep can be provided with a plurality of projections with a narrowed pitch along the steep curvature.
According to another feature of the present invention, the projections are formed at approximately equal angular spacings throughout the wrap portion from the radially inner side to the radially outer side.
With the above-described arrangement, the pitch of the projections in the spiral direction becomes narrow at the radially inner side but wide at the radially outer side. Thus, a radially inner part of the wrap portion where the radius of curvature of the wrap portion is small and hence the curvature thereof is steep can be provided with a plurality of projections with a narrowed pitch along the steep curvature.
According to another feature of the present invention, the projections are provided only on either one of the mutually opposing inner and outer peripheral surfaces of the wrap portions of the one scroll member and the other scroll member. Accordingly, the projections can be disposed to face a smooth peripheral surface of the mating wrap portion.
According to another feature of the present invention, the projections are provided in any one manner selected from among a manner in which the projections are provided on the inner peripheral surface and the outer peripheral surface of the wrap portion of the one scroll member, a manner in which the projections are provided on the inner peripheral surface and the outer peripheral surface of the wrap portion of the other scroll member, a manner in which the projections are provided on the inner peripheral surface of the wrap portion of the one scroll member and on the inner peripheral surface of the wrap portion of the other scroll member, and a manner in which the projections are provided on the outer peripheral surface of the wrap portion of the one scroll member and on the outer peripheral surface of the wrap portion of the other scroll member. In any of these cases, the projections can be disposed to face a smooth peripheral surface of the mating wrap portion.
According to another feature of the present invention, the top of each projection has a width W1 in the range of 0 mmxe2x89xa6W1xe2x89xa62 mm. Accordingly, the tops of the projections can readily be crushed or worn when contacting the opposing peripheral surface of the wrap portion. Therefore, the tops of the projections can become fit to the opposing peripheral surface of the wrap portion without strongly contacting it many times.
According to another feature of the present invention, the projections satisfy the following condition:
S1 less than S2
where S1 is a gap defined between the top of each of the projections provided on the inner peripheral surface of the wrap portion of one of a driven scroll member and the outer peripheral surface of the wrap portion of a fixed scroll member when the projections approach the outer peripheral surface, and S2 is a gap defined between the top of each of the projections provided on the outer peripheral surface of the wrap portion of the driven scroll member and the inner peripheral surface of the wrap portion of the fixed scroll member when the projections approach the inner peripheral surface.
With the above-described arrangement, when contact occurs between the radially opposing wrap portions, the inner peripheral surface of the wrap portion of the driven scroll member contacts the outer peripheral surface of the wrap portion of the fixed or follower scroll member before the outer peripheral surface of the former wrap portion contacts the inner peripheral surface of the latter wrap portion. Through this contact, force acts on the driven scroll member so as to rotate it in the same direction as that of rotating force. Thus, the driven scroll member is pressed in the direction of rotating force, so that backlash can be eliminated.
According to another feature of the present invention, the projections are provided on the wrap portion exclusive of the radially innermost part thereof. Accordingly, the projections can be provided only on a part of the entire length of the wrap portion where projections are needed to increase the degree of hermeticity in the compression chambers.
According to another feature of the present invention, the projections are formed only on a limited axial part of the wrap portion on the end plate away from the end plate.
With the above-described arrangement, for example, when one of the scroll members performs an orbiting motion, the projections on the one scroll member can be brought closest to or into contact with the wrap portion of the other scroll member at the trapping position of the compression chambers. Thus, the degree of hermeticity in the compression chambers can be increased by the projections. Further, because the projections are formed only on a limited axial part of the wrap portion away from the end plate, the axial length of the projections can be reduced, and noise generated by the projections can be minimized.
According to another feature of the present invention, the projections are formed only on a radially inner part of the wrap portion in the spiral direction, and the wrap portion has a non-projection forming region at the radially outer end thereof.
With the above-described arrangement, for example, the smooth peripheral surfaces of the wrap portions can be brought closest to or into contact with each other at the trapping position of compression chambers defined at the radially outermost side of the wrap portion. Accordingly, it is possible to favorably seal the radially outer compression chambers that have a significant effect on the volumetric efficiency during compression.
According to another feature of the present invention, the non-projection forming region is a part of the wrap portion corresponding to approximately one turn of the wrap portion that spirals radially inward from a compression starting position at which the wrap portion of the one scroll member and the wrap portion of the other scroll member come closest to each other at the radially outermost side.
With the above-described arrangement, for example, the sealing performance required for the radially outer compression chambers at the compression starting position and so forth can be improved. Further, because the non-projection forming region is provided over a length corresponding to approximately one turn of the wrap portion from the compression starting position toward the radially inner side, the smooth peripheral surfaces of the wrap portions can surely be brought closest to or into contact with each other at one point on the radially outer side. Accordingly, noise generated by the projections at the radially inner side can be surely blocked at the point where the smooth peripheral surfaces come closest to or in contact with each other and thus prevented from leaking to the outside.